Honor default C compiler

Suppress compilation warnings that occur when characters with values
> 127 are assigned to char variables on x86 platforms. Since x86(-64)
treats char as signed by default and there is no 'unsigned' support at
the moment, these assignments trigger signedness warnings. This commit
adds a compiler option to suppress these warnings.

Author: jserv

Makefile

@@ -1,4 +1,3 @@
-CC ?= gcc
 CFLAGS := -O -g \
 	-std=c99 -pedantic
 
@@ -14,7 +13,8 @@ CFLAGS_TO_CHECK := \
 	-Wno-strict-prototypes \
 	-Wno-declaration-after-statement \
 	-Wno-format \
-	-Wno-format-pedantic
+	-Wno-format-pedantic \
+	-Wno-overflow
 
 SUPPORTED_CFLAGS :=
 # Check if a specific compiler flag is supported, attempting a dummy compilation